The radiotherapy which treats a tumor by exposing radiation is conventionally known. The radiotherapy mainly includes three steps of acquiring diagnostic images by an image diagnostic apparatus, a radiation treatment planning, and the treatment by a radiation treatment apparatus.
Specifically, medical images are previously acquired in the radiotherapy for specifying a tumor area by an X-ray CT (calculated tomography) apparatus, an MRI (magnetic resonance imaging) apparatus, or a nuclear medicine diagnosis apparatuses such as a PET (positron emission calculated tomography) apparatus or a SPECT (single photon emission calculated tomography) apparatus.
Next, the radiation treatment planning is carried out. Specifically, the tumor to be treated and the normal tissues, to which an exposure of radiation is not desirable, are extracted from the medical images acquired by an image diagnostic apparatus. Subsequently, exposure conditions of radiation, such as an exposure range, a direction of exposure and an exposure intensity, are decided as a treatment plan based upon the extraction result. An exposure of radiation to the normal tissues cannot be avoided. Therefore, it is important to plan the exposure conditions of radiation so that an adverse effect does not arise as much as possible. For this reason, a radiation treatment planning requires analytical estimations, such as a DVH (Dose Volume Histogram), for estimating an adverse effect to the normal tissues and a curative effect as well as visual estimations with displaying a dose distribution on a medical image. The DVH is a graph showing a dose of radiation to each volume of a tumor tissue to be treated and the normal tissues.
In recent years, in order to decide upon more detailed conditions, a radiation treatment planning system which supports a radiation treatment planning is proposed. In the conventional radiation treatment planning system, anatomical information is defined based on medical images acquired by an image diagnostic apparatus, and exposure conditions of radiation, such as a direction of exposure, an exposure position, and a dose distribution, are calculated according to the defined anatomical information. Furthermore, the estimation of whether the calculated exposure conditions of radiation are appropriate is carried out.
For such a plan of the dose distribution of radiation and the like, the regions made by adding various margins to the tumor area have been defined conventionally. Specifically, the four regions of the GTV (Gross Tumor Volume), the CTV (Clinical Target Volume), the ITV (Internal Target Volume) and the PTV (Planning Target Volume) have been defined.
The GTV is a region judged that a tumor exists obviously by diagnosis of medical images. A portion in which a tumor invasion is suspected is also included in the GTV as long as it can be recognized on a medical image. The CTV is a region made by adding a minute invaded portion, which cannot be recognized on a medical image, to the GTV. The ITV is a target volume made by adding an IM (Internal Margin), which is a margin area in consideration of a movement of an organ, to the CTV. The PTV is a region made by adding an SM (Setup Margin) to the ITV three dimensionally in consideration of a degree in inaccuracy with regard to a positioning of a patient and a beam.
Then, the proper doses of radiations can be calculated for the respective tumor regions to which these margins have been added. For example, the exposure conditions of radiation can be set up so that a radiation having a sufficient dose not less than 95% may be exposed to not less than 99% of the CTV. Moreover, a model formula for calculating the margin to the PTV is also proposed. For example, a model formula for calculating the margin to the PTV required in order that the minimum dose in the CTV may exceed 95% of a prescribed dose in 90% of patients is known. Note that, in order to also include the periphery of the PTV in the 95% dose area, it is necessary to further add about 5 to 8×10−3 [m] of a margin to the PTV to set up the exposure field of radiation.
After the exposure conditions of radiation has been decided upon as a radiation treatment planning by the dose calculation for every tumor area, it becomes possible to carry out a radiation treatment using a radiation treatment apparatus.